Mixed PMDI/solid novolac resin binders for the production of wood composite products

ABSTRACT

This invention relates to a process for the production of composite wood products. This process comprises a) applying a binder composition to wood particles, and b) molding or compressing the wood particles treated with the binder to form a composite wood product. Suitable binder compositions comprise a polymethylene poly(phenyl isocyanate) and a solid novolac resin.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a process for producing wood compositematerial by combining wood particles with a mixed polymethylenepoly(phenylisocyanate)/solid novolac phenolic resin binder composition,followed by molding or compressing the combined wood particles and thebinder composition.

[0002] Composite materials such as oriented stand board, particle boardand flake board are generally produced by blending or sprayinglignocellulose materials such as wood flakes, wood fibers, woodparticles, wood wafers, strips or strands, pieces of wood or othercomminuted lignocellulose materials with a binder composition while thematerials are tumbled or agitated in a blender or like apparatus. Afterblending sufficiently to form a uniform mixture, the materials areformed into a loose mat, which is compressed between heated platens orplates to set the binder and bond the flakes, strands, strips, pieces,etc., together in densified form. Conventional processes are generallycarried out at temperatures of from about 120 to 225° C. in the presenceof varying amounts of steam generated by liberation of entrainedmoisture from the wood or lignocellulose materials. These processes alsogenerally require that the moisture content of the lignocellulosematerial be between about 2 and about 20% by weight, before it isblended with the binder.

[0003] Plywood production is accomplished by roll coating, knifecoating, curtain coating, or spraying a binder composition onto veneersurfaces. A plurality of veneers are then laid-up to form sheets ofrequired thickness. The mats or sheets are then placed in a heated pressand compressed to effect consolidation and curing of the materials intoa board.

[0004] Binder compositions which have been used in making such compositewood products include phenol formaldehyde resins urea formaldehyderesins and isocyanates. See, for example, James B. Wilson's paperentitled, “Isocyanate Adhesives as Binders for Composition Board” whichwas presented at the symposium “Wood Adhesives—Research, Applicationsand Needs” held in Madison, Wis. on Sep. 23-25, 1980, in which theadvantages and disadvantages of each of these different types of bindersare discussed.

[0005] Isocyanate binders are commercially desirable because they havelow water absorption, high adhesive and cohesive strength, flexibilityin formulation, versatility with respect to cure temperature and rate,excellent structural properties, the ability to bond withlignocellulosic materials having high water contents, and noformaldehyde emissions. The disadvantages of isocyanates are difficultyin processing due to their high reactivity, adhesion to platens, lack ofcold tack, high cost and the need for special storage. U.S. Pat. No.3,870,665 and German Offenlegungsschrift No. 2,109,686 disclose the useof polyisocyanates (and catalysts therefor) in the manufacture ofplywood, fiberboard, compression molded articles, as well as varioustechnical advantages when used as binders.

[0006] It is known to treat cellulosic materials with polymethylenepoly(phenyl isocyanates) (“polymeric MDI”) to improve the strength ofthe product. Typically, such treatment involves applying the isocyanateto the material and allowing the isocyanate to cure, either byapplication of heat and pressure (see, e.g., U.S. Pat. Nos. 3,666,593,5,008,359, 5,140,086, 5,143,768, and 5,204,176) or at room temperature(see, e.g., U.S. Pat. Nos. 4,617,223 and 5,332,458). While it ispossible to allow the polymeric MDI to cure under ambient conditions,residual isocyanate groups remain on the treated products for weeks oreven months in some instances. It is also known to utilize toluylenediisocyanate for such purposes.

[0007] Isocyanate prepolymers are among the preferred isocyanatematerials which have been used in binder compositions to solve variousprocessing problems, particularly adhesion to press platens and highreactivity. U.S. Pat. No. 4,100,328, for example, disclosesisocyanate-terminated prepolymers which improve product release from amold. U.S. Pat. No. 4,609,513 also discloses a process in which anisocyanate-terminated prepolymer binder is used to improve productrelease. A binder composition in which a particular type of isocyanateprepolymer is used to improve adhesiveness at room temperature isdisclosed in U.S. Pat. No. 5,179,143.

[0008] A major processing difficulty encountered with isocyanate bindersis the rapid reaction of the isocyanate with water present in thelignocellulosic material and any water present in the binder compositionitself. One method for minimizing this difficulty is to use onlylignocellulosic materials having a low moisture content (i.e., amoisture content of from about 3 to about 8%). This low moisture contentis generally achieved by drying the cellulosic raw material to reducethe moisture content. Such drying is, however, expensive and has asignificant effect upon the economics of the process. Use of materialshaving low moisture contents is also disadvantageous because panels madefrom the dried composite material tend to absorb moisture and swell whenused in humid environments.

[0009] Another approach to resolving the moisture and isocyanatereactivity problem is disclosed in U.S. Pat. No. 4,546,039. In thisdisclosed process, lignocellulose-containing raw materials having amoisture content of up to 20% are coated with a prepolymer based on adiphenylmethane diisocyanate mixture. This prepolymer has a freeisocyanate group content of about 15 to about 33.6% by weight and aviscosity of from 120 to 1000 mPa·s at 25° C. This prepolymer isprepared by reacting (1) about 0.05 to about 0.5 hydroxyl equivalents ofa polyol having a functionality of from 2 to 8 and a molecular weight offrom about 62 to about 2000 with (2) one equivalent of a polyisocyanatemixture containing (a) from 0 to about 50% by weight of polyphenylpolymethylene polyisocyanate and (b) about 50 to about 100% by weightisomer mixture of diphenylmethane diisocyanate containing 10 to 75% byweight of 2,4′-isomer and 25 to 90% by weight of 4,4′-isomer.

[0010] U.S. Pat. No. 5,002,713 discloses a method for compressionmolding articles from lignocellulosic materials having moisture contentsof at least 15%, generally from 15 to 40%. In this disclosed method, acatalyst is applied to the lignocellulosic material. A water resistantbinder is then applied to the lignocellulose with catalyst and thecoated materials are then compression shaped at a temperature of lessthan 400° F. to form the desired composite article. The catalyst is atertiary amine, an organometallic catalyst or a mixture thereof. Thebinder may be a hydrophobic isocyanate such as any of the polymericdiphenylmethane diisocyanates, m- and p-phenylene diisocyanates,chlorophenylene diisocyanates, toluene diisocyanates, toluenetriisocyanates, triphenylmethane triisocyanates,diphenylether-2,4,4′-triisocyanate and polyphenol polyisocyanates. Thecatalyst is included to ensure that the isocyanate/water reaction is notslowed to such an extent that the pressing time necessary to produce themolded product is significantly increased.

[0011] Pressing of wafer board, oriented strand board, and parallelstrand lumber using steam injection and a conventional binder such as aurea-formaldehyde resin or a polymeric diphenylmethane diisocyanate(MDI) is known. Examples of such known pressing processes are disclosedin U.S. Pat. Nos. 4,684,489; 4,393,019; 4,850,849; and 4,517,147. Theseprocesses yield a product having satisfactory physical properties if thebinder is completely cured.

[0012] The completeness of binder cure may, of course, be determined bydestructive testing of samples which have been permitted to cure forvarying amounts of time under the process conditions. The cure time tobe used during the production process is determined on the basis of thesample which had completely cured in the least amount of time. Thedisadvantages of this method are readily apparent. Valuable product isdestroyed in the testing. Further, any variation in wood composition,extent of binder dispersion on the wood particles, etc. or processingconditions which would affect the rate of binder cure are not taken intoconsideration in the above-described method.

[0013] Binding compositions comprising urea extended polyisocyanatesderived from a combination of a polyisocyanate and urea which is insolution with water, and the process for preparing the bindingcompositions is disclosed in U.S. Pat. No. 5,128,407. This referencealso describes a process for preparing a composite material fromcomminuted particles or veneers of a lignocellulose material comprisingcoating the particles or veneers with these binding compositions.

[0014] A process for producing compression molded articles oflignocellulose type materials by use of an organic polyisocyanatecompound as a binder is disclosed by U.S. Pat. No. 5,744,079. Thebinders comprise (A) an organic polyisocyanate such as, for example, MDIor PMDI, (B) an aqueous emulsion of a wax having a melting point rangingfrom 50° C. to 160° C., (C) an organic phosphate ester derivative, and(D) optionally, water.

[0015] It has been known that organic polyisocyanate resins haveexcellent adhesion properties and workability as the adhesive forthermo-compression molded articles such as particle boards andmedium-quality fiber boards produced from a lignocellulose type materialsuch as wood chips, wood fibers, and the articles exhibit excellentphysical properties. However, the excellent adhesiveness of the organicpolyisocyanate resins causes disadvantage that the compression moldedarticle adheres firmly to the contacting metal surface of the heatingplate in a continuous or batch thermo-compression process.

[0016] To solve the disadvantages of the undesired adhesion to theheating plate, it is required that a releasing agent is preliminarilysprayed onto the heating plate surface to form a releasing layer.Japanese Patent Publication No. 3-21321 discloses a method differentfrom the external releasing agent spray, in which a mixture of anorganic polyisocyanate and a mineral wax is sprayed onto thelignocellulose type material prior to thermo-compression molding.Japanese Patent laid open application No. 4-232004 discloses a method ofthermo-compression molding of a lignocellulose type material by additionof a neutral ortho-phosphate ester as a compatibilizing agent, the waxand the polyisocyanate.

[0017] The large scale industrial manufacture of composite materialswhich are bonded exclusively with polyisocyanates have previously beenlimited. The use of some of the polyisocyanates, particularly the betterperforming isocyanates, such as polymethylene diisocyanate has beenlimited by their cost. Because of the cost constraints, the level of useof these expensive isocyanates is kept low for a given material. Oneapproach to the use of levels of these isocyanates has involved chainextending the isocyanate with inexpensive extenders.

[0018] U.S. Pat. No. 4,944,823 describes a composition for bonding solidlignocellulosic materials. Suitable binder formulations are based on thereactive mixture of an isocyanate and a carbohydrate material. These areboth effective and inexpensive, and eliminate health hazards associatedwith the use of formaldehyde. Carbohydrate materials include, forexample, sugars and starches, in the presence or absence of other activematerials. These carbohydrates are mixed with a liquid diisocyanate andapplied to the wood, which is then pressed to form a composite product.

[0019] Binder compositions comprising phenolic resins andpolyisocyanates are known and described in, for example, U.S. Pat. Nos.3,905,934, 4,293,480, 4,602,069, 4,683,252, 5,001,190, 5,101,001 and5,733,952, and WO 88/03090 and WO 89/07626. These binder compositionsare disclosed as being suitable for foundry cores and molds. Thematerials are typically applied in an organic solvent and cured mostoften in the presence of gaseous amine vapors.

[0020] U.S. Pat. No. 3,905,934 discloses dialkyl phthalate ester solventsystems for phenolic resin-polyisocyanate binder systems. The phenolicresins are preferably benzylic ether resins, including novolac resins.These binder compositions are described as improving the ultimatetensile strength of the resultant foundry core products.

[0021] Phenolic resin and polyisocyanate binder systems containing aphosphorus component are set forth in U.S. Pat. Nos. 4,602,069 and4,683,252. The binder compositions of U.S. Pat. No. 4,602,069 require aphosphorus based acid such as, for example, metaphosphoric,hypophosphoric, orthophosphoric, pyrophosphoric or polyphosphoric acid,or phosphorous, hydrophosphorous or pyrophosphorous acid or an organicderivative of these compounds, and optionally, an acid halide and/or abase. U.S. Pat. No. 4,683,252 describes binder comprising a phenolicresin, a polyisocyanate and an organohalophosphate. Novolacs and resolesare disclosed by both of these patents as suitable phenolic resins.

[0022] U.S. Pat. No. 5,001,190 and PCT application WO 88/03090 disclosea process for filling a space within a structure with a polyurethanecomposite in the presence of water. Suitable polyurethane compositescomprise (a) adding a coarse aggregate to the space in the structure tobe filled, (b) adding a polyurethane binder to the aggregate, whereinthe binder comprises (i) a phenolic resin component comprising a resolephenolic resin and a hydrophobic solvent system, and (ii) apolyisocyanate component comprising an aromatic polyisocyanate and ahydrophobic solvent, and (iii) a urethane promoting catalyst.

[0023] Foundry binders based on phenolic resole resins andpolyisocyanates are described in U.S. Pat. No. 5,101,001 and 5,733,952,and PCT application WO 89/07626. The compositions of U.S. Pat. No.5,733,952 also comprise an epoxy resin and, preferably, paraffinic oil.Polymerized linseed oil is utilized in the binders of WP 89/07626.

[0024] Isocyanates are known to be suitable components for treatingcellulosic fiber and wood products. Some processes for this treatmentare described in, for example, U.S. Pat. Nos. 5,179,143 and 5,674,568.The binders of U.S. Pat. No. 5,179,143 comprise polyisocyanates,compounds containing at least two isocyanate reactive hydrogen atoms andalkylene carbonates. The binders for modified cellulosic products ofU.S. 5,674,568 comprise a polymethylene poly(phenylisocyanate), water,and an organic compound having a hydroxy functionality of from 2 to 8and a molecular weight of about 60 to 8000 and being selected from thegroup consisting of ester group-free polyhydric alcohols, polyetherpolyols and mixtures thereof.

[0025] Binders comprising polyisocyanates and phenolic resins are knownand described as being suitable for preparing wood composite products byU.S. Pat. Nos. 4,209,433, 4,961,795, and 5,217,665. Suitable phenolicresins disclosed by these references are resole resins. U.S. Pat. No.4,209,433 requires that the polyisocyanate be added to the woodparticles prior to the application of the phenolic resin, therebyproducing enhanced adhesive characteristics. The binder compositions ofU.S. Pat. No. 4,961,795 may be cured with a curing agent comprising anester, a lactone or an organic carbonate, which may be moderated by analiphatic mono- or polyhydric alcohol.

[0026] A method of producing waferboard is described by U.S. 5,217,665.This method comprises applying first a liquid phenol formaldehyde resinto the surface of the wafers, then a powdered phenol formaldehyde resin.This is followed by forming layup and pressing at elevated temperatureand pressure using steam pressing techniques to consolidate the layupinto a board and to set the phenolic resin adhesive.

[0027] It is the purpose of this invention to make a mixed adhesive forwood composite manufacture that utilizes the strength of both thepolyisocyanate and phenolic resins. These compositions do not containorganic solvents and do not require catalysts to cure. The curingtemperatures are lower than that of the phenolic alone. Typically,novolac resins are cured by adding a compound which generatesformaldehyde. The compositions of the present invention contain noformaldehyde. The water resistance of the composites is better than thatof the phenolic alone. Less polyisocyanate can be used which results ina cost savings, and the tendency of the adhesives to stick to theplatens is reduced.

SUMMARY OF THE INVENTION

[0028] This invention relates to a process for the production of woodcomposite materials comprising A) combining wood particles with a bindercomposition, and B) molding or compressing the combination of woodparticles and binder composition formed in A). The compression ormolding typically occurs at pressures of from about 200 to 1000 psi(preferably 300 to 700 psi) for about 2 to 10 (preferably 4 to 8)minutes at temperatures of from about 120° C. to 220° C. (preferably 150to 200° C.). Suitable binder compositions to be combined with the woodparticles in step A) consist essentially of:

[0029] (1) a polymethylene poly(phenylisocyanate) component having afunctionality of about 2.1 to about 3.5, an NCO group content of about25 to 33%, and a monomer content of from about 30% to about 90% byweight, wherein the content of the monomer comprises up to about 5% byweight of the 2,2′-isomer, from about 1% to about 20% by weight of the2,4′-isomer, and from about 25% to about 65% by weight of the4,4′-isomer, based on the entire weight of the polyisocyanate; and

[0030] (2) a solid novolac resin.

[0031] In accordance with the present invention, wood particles arecombined with from about 1 to 25% by weight, preferably from 2 to 10% byweight, most preferably with from 3 to 8% by weight of the bindercompositions, based on the total weight of the wood composite. Theweight ratio of component A)(2) the solid novolac resin to componentA)(1) the polymethylene poly(phenylisocyanate) is from 2:1 to 10:1,preferably from 3:1 to 7:1.

[0032] When the binders are combined in this ratio, they typically donot flow as the novolac does not dissolve in the polyisocyanate. Also,they are not free flowing powders. Rather, these binders have theconsistency of brown sugar.

DETAILED DESCRIPTION OF THE INVENTION

[0033] Polymeric MDI as used herein, refers to the three-ring and/orhigher ring products derived by the phosgenation of aniline-formaldehydecondensation products.

[0034] Suitable polyisocyanates to be used as component 1) of thecompositions in the present invention include (a) those polymethylenepoly(phenylisocyanate) blends having an NCO group content of about 25%to 33% by weight, and having a viscosity of less than about 2,000 cps at25° C. The polyisocyanates of the present invention have a functionalityof from about 2.1 to about 3.5, preferably 2.3 to 3.0 and mostpreferably of 2.6 to 2.8, and an NCO group content of about 30% to about33%, preferably about 30.5% to about 32.5%, and a monomer content offrom about 30% to about 90% by weight, preferably from about 40% toabout 70%, wherein the content of monomer comprises up to about 5% byweight of the 2,2′-isomer, from about 1 to about 20% by weight of the2,4′-isomer, and from about 25 to about 65% by weight of the4,4′-isomer, based on the entire weight of the blend. The polymeric MDIcontent of these isocyanates varies from about 10 to about 70% byweight, preferably from about 30% to about 60% by weight.

[0035] It is preferred that the polyisocyanates used as component (1) inthe present invention have an average functionality of about 2.3 toabout 3.0, most preferably of about 2.4 to about 2.8, and a monomercontent of preferably 40 to 80%, most preferably of 40 to 70% by weight.The content of monomeric MDI preferably comprises less than 1 % byweight of the 2,2′-isomer of MDI, less than 5% by weight of the2,4′-isomer of MDI and from about 30 to about 60% by weight of the4,4′-isomer of MDI, based on the entire weight of the polyisocyanate.Preferred polyisocyanates have viscosities of 10 to 1000 cps, morepreferred polyisocyanates have viscosities of 40 to 400, and mostpreferred polyisocyanates have viscosities of 100 to 300 cps.

[0036] A preferred polymethylene poly(phenylisocyanate) blend has afunctionality of from 2.2 to 2.4, an NCO group content of from about31.2 to about 32.8% by weight, and a monomer content of from about 55%to about 80%, wherein the content of monomer comprises no more thanabout 3% by weight of the 2,2′-isomer, from about 15% to about 20% byweight of the 2,4′-isomer and from about 40% to about 55% by weight ofthe 4,4′-isomer, based on the entire weight of the blend. Thispolyisocyanate blend comprises from about 20 to about 45% by weight ofpolymeric MDI.

[0037] Most preferred polyisocyanates include, for example,polymethylene poly(phenylisocyanate) blends having an averagefunctionality of from about 2.5 to about 3.0, preferably about 2.6 toabout 2.8, an NCO group content of about 30 to 32% by weight, and amonomer content of from about 40 to 50% by weight, wherein the contentof monomer comprises no more than about 1-% by weight of the2,2′-isomer, from about 2 to about 10% by weight of the 2,4′-isomer andfrom about 35 to about 45% by weight of the 4,4′-isomer, based on theentire weight of the blend. This isocyanate blend comprises from about50 to about 60% by weight of polymeric MDI.

[0038] Suitable polyisocyanates for component (1) of the presentinvention also include, for example, mixtures of polyisocyanate blendsas described above with adducts of MDI including, for example,allophanates of MDI as described in, for example, U.S. Pat. Nos.5,319,053, 5,319,054 and 5,440,003, the disclosures of which are hereinincorporated by reference, and carbodiimides of MDI as described in, forexample, U.S. Pat. Nos. 2,853,473, 2,941,966, 3,152,162, 4,088,665,4,294,719 and 4,244,855, the disclosures of which are hereinincorporated by reference.

[0039] Phenolic resins, obtained by the condensation of a phenoliccompound with an aldehyde, are generally divided into two categories,the “novolac” resins and the “resole” resins or A-stage resins and theirmore highly polymerized derivatives, the “resitole” or B-stage resins.Novolac resins are permanently soluble, fusible resins in which thepolymer chains have phenolic end-groups. They react to form crude toinsoluble, infusible products upon the addition of a source offormaldehyde, such as hexamethylenetetraamine or paraform. Novolacresins have an excess of phenol. Resole and resitole resins are preparedgenerally using an alkaline catalyst with excess formaldehyde and resultin polymers having pendant methylol groups. In the resitole stage, theresins are characterized by high viscosity. Since each methylol groupconstitutes a potential cross-linking site, the resole and resitoleresins are readily converted to the cross-linked, infusible polymers byheating. Conversely, these resins are highly unstable.

[0040] Suitable solid novolac resins to be used as component (2) in thepresent invention include, for example, the phenolic resins in which thephenolic nuclei are joined by methylene bridges located at the ortho-and para-positions relative to the phenolic hydroxyl group. It isgenerally accepted that conventional acidic catalysts produce resinswith a predominance of 4,4′- and 4,2′-linkages, although some2,2′-linkages are also formed. Acid catalyzed resins have not been foundfully acceptable where fast curing results are required as a result ofthe 4,4′- and 4,2′-linkages. Recently, novolac resins have been preparedwhich contain significant proportions of 2,2′-linkages using metal oxideor metal salt catalysts. This polymerization process is frequentlyreferred to as an “ionic” polymerization. These ortho-resins cure fasterand produce cross-linked phenolic resins of improved mechanicalproperties. Theoretically, the more ordered structure of the polymermolecule is obtained with 2,2′-linkages. The formation of phenolicresins of this type has, however, been limited to methods in which anexcess of phenol is employed, which is necessary to prevent gelation ofthe resins during polymerization.

[0041] Suitable phenolic resins for the present invention compositionsare (a) a mixture of dimethylol compounds having the formulas:

[0042] wherein:

[0043] R: represents a hydrogen atom or a phenolic substituent meta tothe phenolic hydroxyl group, said component (a)(iii) being a minorconstituent in the mixture; and

[0044] (b) at least one compound corresponding to the formula:

[0045] wherein:

[0046] each R: independently represents a hydrogen atom or a phenolicsubstituent meta to the phenolic hydroxyl group; and

[0047] (c) higher molecular weight condensation products of said mixturehaving the general formula:

[0048] wherein:

[0049] R: represents a hydrogen atom or a phenolic substituent meta tothe phenolic group;

[0050] X: represents an end group from the group consisting of hydrogenand methylol, wherein the molar ratio of methylol to hydrogen end groupsis less than 1:1; and

[0051] m and n: are each independently selected from a number between 0and 20.

[0052] The phenolic compositions of the present invention as well asother highly valuable phenolic condensation products are prepared by aprocess which comprises reacting at temperatures below about 130° C. aphenol with an aldehyde under substantially anhydrous conditions in theliquid phase in the presence of a metal ion as the catalyst, thepreferred metal ion being a divalent metal ion such as zinc, cadmium,manganese, copper, tin, magnesium, cobalt, lead, calcium and barium.

[0053] These solid novolac resins are typically prepared by thepolymerization reaction of a suitable phenol group containing compoundwith an aldehyde, wherein a stoichiometric excess of the phenol groupcontaining compound is present. Suitable phenolic components includenonyl phenol, as well as virtually any of the phenols which are notsubstituted at either the two ortho-positions or at one ortho and theparapositions. It is necessary that these positions be unsubstituted forthe polymerization reaction with the aldehyde to occur. Any one, all, ornone of the remaining carbon atoms of the phenol ring can besubstituted. The nature of the substituent can vary widely, and it isonly necessary that the substituent not interfere in the polymerizationof the aldehyde with the phenol at the ortho- and/or para-positions,substituted phenols employed in the formation of the novolac resinsinclude, for example, alkyl-substituted phenols, aryl-substitutedphenols, cyclo-alkyl-substituted phenols, alkenyl-substituted phenols,alkoxy-substituted phenols, aryloxy-substituted phenols, andhalogen-substituted phenols, the foregoing substituents containing from1 to 26 and preferably from 1 to 12 carbon atoms. Specific examples ofsuitable phenols include, for example, phenol, 2,6-xylenol, o-cresol,m-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 2,3,4-trimethyl phenol,3-ethyl phenol, 2,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol,p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol 3,5-dicyclohexylphenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol,3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol,3-methyl-4-methoxy phenol, and p-phenoxy phenol. Such phenols can bedescribed by the formula:

[0054] wherein:

[0055] A, B, and C: each independently represent hydrogen, hydroxylradicals, hydrocarbon radicals, oxyhydrocarbon radicals or a halogenradical.

[0056] Also, suitable phenolic compounds are those compounds containinga second phenolic group such as, for example, catechol, resorcinol andhydroquinone.

[0057] The aldehydes reacted with the phenol can include any of thealdehydes theretofore employed in the formation of phenolic resins suchas, for example, formaldehyde, acetaldehyde, propionaldehyde,furfuraldehyde, and benzaldehyde. In general, the aldehydes employedhave the formula: R′CHO wherein R′ is a hydrogen or a hydrocarbonradical of 1 to 8 carbon atoms. Formaldehyde is the most preferredaldehyde.

[0058] The novolac resins of the present invention are typicallyprepared by reacting a stoichiometric excess of the phenol groupcontaining compound with a suitable aldehyde, thereby forming a solidnovolac resin. Additional information relative to the preparation of thenovolac resins can be found in, for example, Encyclopedia of ChemicalTechnology by Kirk Othmer, Fourth Edition, Volume 18, pp. 606-609.

[0059] Known catalysts for accelerating the isocyanate addition reactionmay in principle be used in forming these binder compositions. The useof catalysts is not, however, necessary to the present invention.Suitable catalysts for this purpose include, for example, tin compoundssuch as dibutyl tin dilaurate or tin(II) octoate; and tertiary aminessuch as, for example, triethylene diamine, dimethylethyl amine,pyridine, 4-phenylpropyl pyridine, bis(N,N-dimethylaminoethyl) ether,N,N′-dimethylaminoethyl-N-methyl ethanolamine, N,N-dimethylaminoethylmorpholine, quinoline, morpholine, N-methyl morpholine, etc. Othercatalysts are described in “Kunstoff Handbuch”, Volume VlI, published byBecker and Braun, Carl Hanser Vernag, Munich, 1983 on pages 92-98. Thecatalysts are used, if at all, in a quantity of about 0.001 to 10% byweight, preferably about 0.002 to 0.1% by weight, based on the totalquantity of reactants.

[0060] Other optional additives and/or auxiliary agents which may beincluded in the binding compositions of the present invention include,for example, wax emulsions for reduced water absorption, preservatives,surface active additives, e.g., emulsifiers and stabilizers, moldrelease agents such as, for example, zinc stearate, etc. As stabilizingagents which reduce swelling and water absorption, there may bementioned sodium chloride, sodium sulfate, paraffin, fatty acids ortheir salts such as zinc stearate and other similar materials. At thesame time, paraffin and fatty acids and their salts may serve as releaseagents. Use of other active materials may shorten pressing and curingtime.

[0061] As indicated above, the percentages of ingredients in the woodbinder compositions according to the present invention can vary widelyaccording to needs and conditions of a particular application. Ingeneral, however, quantities in the following ranges have been foundsuitable, bearing in mind that the other active materials may compriseone or more of the catalysts, stabilizing agents and release agents.

[0062] A preferred formulation for the composite products, such asparticle board, comprises a blend of novolac resins, together withisocyanate (PMDI), with or without stabilizing agent, catalyst orrelease agent. The binder formulation for a particular product willdepend upon wood species, requirements of physical properties of theresultant product, and pressing conditions, For example, a formulationrange for Douglas fir commercial furnish requirements for interiorparticle board pressed at a press platten temperature of 350° F. for 4.4minutes press time, to give a high quality commercial product is asfollows: Components Preferred range Novolac Resin 50-70% PMDI  5-35%Stabilizer 20-35% Wax  3-10%

[0063] This binder formulation may be used in an amount of 1 to 25% byweight, expressed as a percentage of the total wood weight, or about0.25 to 8.0% of PMDI based on the wood weight. Preferably, the quantityof binder formulation based on the weight of the wood is about 2 to 10%,depending on the configuration of the particulate wood and therequirements of the products. Also, if a small amount of isocyanate isused in the binder formulation (e.g., about 10 to 20% based on the totalbinder formulation, providing a relatively dry powder), then relativelygreater proportions of binder formulation will be used (e.g., 8 to 10%binder formulation, or 1 to 2% isocyanate based on the wood weight). Onthe other hand, when relatively small quantities of binder formulationare used (e.g., 2 to 6% binder formulation) then the quantity ofisocyanate in the powdery binder should be somewhat greater (e.g., 25 to35%) to provide sufficient bonding, this provides a minimum percentageof isocyanate based on the quantity of wood of about 0.5 to 2%. Ingeneral, using a preferred powdery binder formulation, the maximumamount of isocyanate present will be about 20% based on the binder, or2% based on the wood when 10% binder is used.

[0064] Although much less preferred, it is also possible to make liquidbinder formulations according to the present invention using smallquantities of inert, polar, non-aqueous solvent such as, for example,methylene chloride, or plasticizers such as, for example, butylbenzylphthalate or dioctyl phthalate, or solutions of novolac resins ininert, polar, non-aqueous solvents can also be used. Liquid binderformulations can have limited potlife. Care must also be exercised inminimizing the water content of these dissolved novolac resins becauseof the undesirable reaction between the isocyanate and the water priorto the wood bonding operation.

[0065] Liquid binder formulations according to the present invention canalso be made by first mixing a relatively large quantity of dry novolacresin with a relatively small quantity of isocyanate, letting themixture react to the point where free isocyanate is no longer presentand then adding inert solvent or plasticizer to form a viscous mass.Thus, such a viscous mass can be obtained by first blending isocyanatewith a novolac resin in the ratio of 10 to 50% by weight isocyanate and50 to 90% by weight of powdered novolac, then letting the mixture reactfor 5 to 60 minutes, and finally adding 30 to 70%, based on the weightof the mixture, of inert solvent or plasticizer to obtain a viscous masssuitable for roller spreading on veneers in plywood manufacture.Viscosity can be controlled by adjusting the ratio of components in themixture.

[0066] Binder formulations according to the present invention are madeby blending together the various components in the proper sequence asnoted above. When producing the preferred powdery binders, such blendingpreferably involves vigorous agitation for several minutes, such as in asuitable mill, in order to insure thorough blending of the isocyanatewith the other components. It is preferable to blend together first theisocyanate with the stabilizing agent, catalyst and release agent (ifone or more of these latter components are used) and then to add thenovolac resin. Of course, the blending should be carried out for a timesufficient to produce a homogeneous blend, and under vigorous blendingconditions, this will usually occur after several minutes of vigorousagitation.

[0067] The powdered binder formulations are applied to wood particles inthe manufacture of particle board, wafer board, fiber board, etc., byintermixing a stream of wood particles with a stream of the powderedbinder formulation at the desired ratio and using mechanical agitationwhich is in common usage in the manufacture of composite products suchas particle board. When using powdered binders to make particle board orthe like, the wood may have a wide range of moisture content, i.e., fromabout 0.5 to about 10% by weight, based on the total weight of the woodparticles. However, it is advantageous if the moisture content of thewood particles is relatively low, i.e., on the order of about 1 to 6%,and after initial pressing and prior to final compacting in a hot press,the pre-formed particle board is sprayed with water to increase itsmoisture content to 10 to 11%.

[0068] Alternatively, although less preferred, binders can be addedseparately and subsequently blended together with the wood particles.This is less preferred because, at least in some cases, the twoco-reactants are not intimately mixed in the proper ratios. As soon asthe binder according to the invention comes into contact with wood, itstarts reacting with the water contained in the wood.

[0069] The binder and resultant products are free of formaldehyde andthe composite is produced at a cost competitive to the cost of makingwood products using urea-formaldehyde resin which has the seriousproblem of formaldehyde emission. The binder formulation can also beapplied to wood at higher moisture content which saves energy byreducing the degree of drying normally required prior to pressing.

[0070] The following examples further illustrate details for the processof this invention. The invention, which is set forth in the foregoingdisclosure, is not to be limited either in spirit or scope by theseexamples. Those skilled in the art will readily understand that knownvariations of the conditions of the following procedures can be used.Unless otherwise noted, all temperatures are degrees Celsius and allparts and percentages are parts by weight and percentages by weight,respectively.

EXAMPLES

[0071] The following components were used in the working examples ofthis invention: Isocyanate A: polymethylene poly(phenyl isocyanate)blend having an NCO group content of 31.5% and a viscosity of about 200mPa.s, commercially available from Bayer Corporation Cascophen ®SD-838A: a Novolac resin, commercially available from Borden Chemical,Inc. Varcum ® 29-615: a Novolac resin, commercially available fromOccidental Chemical, Inc. (CAS Registry Number = 40216-08-8) StabilizerA: sebacic acid

[0072] The procedure used to prepare the boards containing the Cascophenand Varcum resins were the same, only differing in the amounts of eachperspective resin (Novolac or Varcum) used in conjunction with theisocyanate. This procedure consisted of two parts, preparation of thebinder, and preparation of the board.

[0073] Procedure for Preparation of Binder

[0074] 200 parts by weight of Isocyanate A were combined with 100 partsby weight of Stabilizer A in a 32-oz. jar and mixed well. Then, 100parts by weight of the solid resin (Novolac or Varcum) was ball-milledand screened using a #40 US-mesh sieve. This material was then placed ina separate container from the mixture of Isocyanate A and Stabilizer A(sebacic acid). The Isocyanate/Stabilizer mixture was added to the driedresin in the amounts shown in the Tables, and burundum cylinders wereadded to the 32-oz. jar. The jar was then rolled on a roller table for 1to 1½ hours. The container was periodically opened and material clingingto the container walls was scraped off. The binder mix was then sievedonce more through a #40 US-mesh sieve and placed in a catch pan. Thecatch pan containing the binder was placed in a dessicator for 3 to 4hours.

[0075] Procedure for Preparation of Boards

[0076] According to the amounts shown in the Tables, particleboardfurnish was placed in a stainless steel bowl (for use in a KitchenAidKSM90 mixer). The binder mixture, now semi-dried, was added in 5 to 10 gincrements, and the furnish was mixed by hand initially to promoteuniform dispersion of the binder to the furnish. The stainless bowl wastransferred to the KitchenAid mixer and mixed at lowest speed for 5minutes. The resin-coated furnish was then placed in an eight inch byeight inch form and pre-pressed by hand. The form was then placed in aCarver Press (Model M), and pressed at 350° F. for four and one halfminutes.

[0077] The resultant boards were tested for Internal Bond Strength andThickness Swell in accordance with ASTM method D1037: EvaluatingProperties of Wood-Base Fiber and Particle Panel Materials. The resultsare set forth in Tables 1 through 3 below. TABLE 1 Example 1 2 Percentof each resin 7:1 7:1 based on total weight Varcum 29-615/ Varcum29-615/ of composite board Isocyanate A Isocyanate A Percent Wood* 91.5%91.5% Percent Sebacic Acid 0.5% 0.5% Curing Temperature 350 400 (° F.)Average Density (pcf) 56.32 53.09 Internal Bond Strength 190 144 (psi)Thickness Swell (%) 17.7 16.1

[0078] TABLE 2 Example 3 4 Percent of each resin 7:1 7:1 based on totalweight Cascophen SD-838A/ Cascophen SD-838A/ of composite boardIsocyanate A Isocyanate A Percent Wood* 91.5% 91.5% Percent Stabilizer0.5% 0.5% Curing Temperature 350 400 (° F.) Average Density (pcf) 52.8752.16 Internal Bond Strength 213 189 (psi) Thickness Swell (%) 17.3 19.1

[0079] TABLE 3 Example 5 6 Percent of each resin 6:2 7:1 based on totalweight Cascophen SD-838A/ Cascophen SD-838A/ of composite boardIsocyanate A Isocyanate A Percent Wood* 91% 91.5% Percent Stabilizer1.0% 0.5% Curing Temperature 400 400 (° F.) Average Density (pcf) 52.4551.14 Internal Bond Strength 242 179 (PSI) Thickness Swell (%) 12.5 30.2

[0080] Although the invention has been described in detail in theforegoing for the purpose of illustration, it is to be understood thatsuch detail is solely for that purpose and that variations can be madetherein by those skilled in the art without departing from the spiritand scope of the invention except as it may be limited by the claims.

What is claimed is:
 1. A process for the production of wood compositematerials comprising: A) combining wood particles with 1 to 25% byweight, based on the total weight of the wood composite, of a bindercomposition consisting essentially of: (1) a polymethylenepoly(phenylisocyanate) having a functionality of about 2.1 to about 3.5,and NCO group content of from about 25 to 33%, and a monomer content offrom about 30% to 90% by weight, wherein the content of the monomercomprises up to about 5% by weight of the 2,2′-isomer, from about 1% upto about 20% by weight of the 2,4′-isomer, and from about 25% to about65% by weight of the 4,4′-isomer, based on the entire weight of thepolyisocyanate: and (2) a solid novolac resin, wherein the weight ratioof component A)(2) to component A)(1) is from 2:1 to 10:1; and B)molding or compressing the combination formed in A), thus forming thewood composite material.
 2. The process of claim 1 , wherein the woodparticles are combined with from 2 to 10% by weight, based on the totalweight of the wood composite, of a binder composition.
 3. The process ofclaim 1 , wherein the wood particles are combined with from 3 to 8% byweight, based on the total weight of the wood composite, of a bindercomposition.
 4. The process of claim 1 , wherein the weight ratio ofcomponent A)(2) to component A)(1) is from 3:1 to 7:1.
 5. The process ofclaim 1 , wherein component A)(1) said polymethylenepoly(phenylisocyanate) has a viscosity of less than about 2,000 cps at25° C.
 6. The process of claim 5 , wherein component A)(1) saidpolymethylene poly(phenylisocyanate) has a functionality of about 2.3 to3.0, an NCO group content of about 30 to 33%, and a monomer content ofabout 40 to 70%.
 7. The process of claim 6 , wherein component A)(1)said polymethylene poly(phenylisocyanate) has a functionality of about2.4 to 2.8, and wherein the content of monomer comprises less than 1% byweight of the 2,2′-isomer of MDI, less than 5% by weight of the2,4′-isomer of MDI and from about 30 to about 60% by weight of the4,4′-isomer of MDI.
 8. The process of claim 1 , wherein component A)(1)said polymethylene poly(phenylisocyanate) comprises a blend having afunctionality of from 2.2 to 2.4, and NCO group content of from about31.2 to about 32.8%, and a monomer content of from about 55 to 80% byweight, wherein the content of monomer comprises no more than about 3%by weight of the 2,2c-isomer of MDI, from about 15 to about 20% byweight of the 2,4′-isomer of MDI and from about 40 to about 55% byweight of the 4,4′-isomer of MDI, based on the entire weight of theblend.
 9. The process of claim 1 , wherein component A)(2) said solidnovolac resin comprises at least one compound selected from the groupconsisting of:

wherein: each R: independently represents a hydrogen atom or a phenolicsubstituent meta to the phenolic hydroxyl group.
 10. The process ofclaim 1 , wherein B) the molding or compressing of the combinationformed in A) occurs at pressures of from about 200 to about 1,000 psifor about 2 to 10 minutes and at temperatures of from about 120 to 225°C.
 11. The process of claim 10 , wherein the pressure ranges from about300 to 700 psi, the time ranges from about 4 to about 8 minutes and thetemperature ranges from about 150 to 200° C.
 12. A process for theproduction of wood composite materials comprising: A) combining woodparticles with (1) a polymethylene poly(phenylisocyanate) having afunctionality of about 2.1 to about 3.5, and NCO group content of fromabout 25 to 33%, and a monomer content of from about 30% to 90% byweight, wherein the content of the monomer comprises up to about 5% byweight of the 2,2′-isomer, from about 1% up to about 20% by weight ofthe 2,4′-isomer, and from about 25% to about 65% by weight of the4,4′-isomer, based on the entire weight of the polyisocyanate; B)coating the combination formed in A) with (2) a solid novolac resin; andC) molding or compressing the coated combination formed in B); whereincomponents (1) and (2) are present in amounts such that there is from 1to 25% by weight, based on the total weight of the wood composite, ofcomponents (1) and (2), and the weight ratio of component (2) tocomponent (1 ) is from 1:3 to 10:1.
 13. The process of claim 12 ,wherein components (1) and (2) are present in amounts such that there isfrom 2 to 10% by weight, based on the total weight of the woodcomposite, of components (1) and (2).
 14. The process of claim 12 ,wherein components (1) and (2) are present in amounts such that there isfrom 3 to 8% by weight, based on the total weight of the wood composite,of components (1) and (2).
 15. The process of claim 12 , wherein theweight ratio of component A)(2) to component A)(1) is from 3:1 to 7:1.16. The process of claim 12 , wherein component A)(1) said polymethylenepoly(phenylisocyanate) has a viscosity of less than about 2,000 cps at25° C.
 17. The process of claim 12 , wherein component A)(1) saidpolymethylene poly(phenylisocyanate) has a functionality of about 2.3 to3.0, an NCO group content of about 30 to 33%, and a monomer content ofabout 40 to 70%.
 18. A process for the production of wood compositematerials comprising: A) combining wood particles with (2) a solidnovolac resin; B) coating the combination formed in A) with (1) apolymethylene poly(phenylisocyanate) having a functionality of about 2.1to about 3.5, and NCO group content of from about 25 to 33%, and amonomer content of from about 30% to 90% by weight, wherein the contentof the monomer comprises up to about 5% by weight of the 2,2′-isomer,from about 1% up to about 20% by weight of the 2,4′-isomer, and fromabout 25% to about 65% by weight of the 4,4′-isomer, based on the entireweight of the polyisocyanate; and C) molding or compressing the coatedcombination formed in B); wherein components (1) and (2) are present inamounts such that there is from 1 to 25% by weight, based on the totalweight of the wood composite, of components (1) and (2), and the weightratio of component (2) to component (1) is from 1:3 to 10:1.
 19. Theprocess of claim 18 , wherein components (1) and (2) are present inamounts such that there is from 2 to 10% by weight, based on the totalweight of the wood composite, of components (1) and (2).
 20. The processof claim 18 , wherein components (1) and (2) are present in amounts suchthat there is from 3 to 8% by weight, based on the total weight of thewood composite, of components (1) and (2).
 21. The process of claim 18 ,wherein the weight ratio of component A)(2) to component A)(1) is from3:1 to 7:1.
 22. The process of claim 18 , wherein component A)(1) saidpolymethylene poly(phenylisocyanate) has a viscosity of less than about2,000 cps at 25° C.
 23. The process of claim 18 , wherein componentA)(1) said polymethylene poly(phenylisocyanate) has a functionality ofabout 2.3 to 3.0, an NCO group content of about 30 to 33%, and a monomercontent of about 40 to 70%.